duplicate values of different two tables with only two common columns

Question

I have two tables with only two columns in common that I want to compare to each other and remove duplicate of the common columns for example TABLE A has 4 columns and table B has 6 columns , I want to get the records of table A , BUT without the records where the rows matches ( when the values of the two common columns matches ) for example in the common two columns in tabe A there is code=x , Nature =y and in table B there is also code=x , Nature =y , so this record should be removed when I fetch the table A records ... I'm using visual studio c# and I didn't know what query to do to fetch these recrods ,any help please